According to Elliotte Freidman, the NHL and NHLPA have agreed to a fairly big change to Rule 48, which was put in place to curb the rash of concussions dogging the NHL.
"A hit resulting in contact with an opponent's head where the head is targeted and the principal point of contact is not permitted."
...has been changed to
"... a hit resulting in contact with an opponent's head where the head was the main point of contact and such contact to the head was avoidable."
This is an interesting shift in the criteria used to judge hits. I felt that the targeting language was too subjective and one's intentions didn't necessarily play out in easily traced physical actions. Good that it's gone, as far as I'm concerned. The Shanahan videos have been using criteria like last minute movement to qualify and judge illegal/legal hits for several years, and according to Freidman the criteria are as follows:
First, whether the player attempted to hit squarely through the opponent's body and the head was not "picked" as a result of poor timing, poor angle of approach or unnecessary extension of the body upward or outward.
Second, whether the opponent put himself in a vulnerable position by assuming a posture that made head contact on an otherwise full body check unavoidable.
Third, whether the opponent materially changed the position of his body or head immediately prior to or simultaneously with the hit in a way that significantly contributed to the head contact.
The first and third are reasonable, but I foresee some trouble with #2. On hits where someone is stretching out over the blue line for a long pass, usually we consider that putting yourself in a vulnerable position. That however DOES NOT make head contact unavoidable. Hip checks, for instance can blow a dude up when he makes himself vulnerable and don't involve body armor with 200 pounds of momentum behind them impacting chins and helmets at 15 MPH. I think they're going to have to be careful in how this is enforced so it's not exploited as an out clause for every headshot that doesn't involve a flying elbow or Raffi Torres (redundant, I know).
Overall I think it's a good change that works to remove the viewer's opinion from judgements on legality. Impartiality is good, and this is a step towards it.